Not Applicable
The invention is a SCARA type robot with counterbalanced arms and tilting base, these features make the invention especially useful for on-site or portable near-field testing of antennas.
A SCARA (Selective Compliance Assembly Robot Arm) robot is a robotic arm structure of two jointed links or arms rotating about parallel vertical axes. One end of the base arm mounts on a shaft or bearing on a base. The base arm is rotated about this shaft or bearing. The other end of the base arm supports an end of the second arm on a shaft or bearing. The second arm is rotated about this shaft or bearing. The axes of both shafts or bearings are parallel and vertical. An end effector, such as a probe, camera, manipulator, etc, is placed at the other end of the second arm. Appropriate rotations of the arms will position the end effector at any given point in a plane. An embodiment of a SCARA is in U.S. Pat. No. 4,392,776 to Shum (1983). This patent has no counterbalancing of either arm.
There are multiple US patents having means to counterbalance robot arms. Most of these patents do not directly apply to SCARA type robots and use springs, pneumatics, or counterweights with multiple links. Some examples are: U.S. Pat. No. 4,954,043 to Yoshida (1990), U.S. Pat. No. 4,229,136 to Panissidi (1980), and U.S. Pat. No. 5,456,130 to Pierson et al. (1995). These arrangements add expense, and complication to the robot arm.
U.S. Pat. No. 5,634,377 Kimura et al. (1997) has a SCARA type robot arm with a counterbalanced second arm. Kimura""s invention has many other features. These features and the counterbalance all relate to improving the dynamic performance and control of the arm. A counterweight or a drive motor for an end effector at the second arm tip provides balancing. There is no counterbalance on the base arm. Movement of the base arm will change the forces on the base and base supporting surface therefore accuracy of the second arm tip location will be effected. If the robot arm assembly is tilted such that the base arm moves in a non-horizontal plane the loads on the base arm drive mechanism will increase.
U.S. Pat. No. 4,775,289 Kazerooni (1988) has a robot arm with a counterbalance arm assembly. The arm assembly is counterbalance about the vertical rotation axis of the base. Therefore arm movements do not change loads into the base. Kazerooni""s invention is very similar to a SCARA arm arrangement with the addition of rotation about a horizontal axis and using a link to rotate the second arm. The second arm is not counterbalanced by itself therefore second arm movement will cause different loads into the base arm affecting accuracy of the second arm tip location. The link used to rotate the second arm limits the second arm rotation. Accurate control of the second arm becomes progressively worse as the angle between the second arm and base arm is further away from 90 degrees. The use of the second arm drive motor as a counterweight limits the location of the drive motor.
The linkage used in an arm-type drafting machine can be used to control the angular orientation of a SCARA end effector relative to the SCARA""s base. Prior to the extensive use of computer aided drafting an arm-type drafting machine was very common in drafting and engineering offices. The base of the arm-type drafting machined is secured to the drafting table. The drafting head is linked via two arms, (similar to a SCARA arrangement), and pulleys and belts to the base. The drafting head keeps its same angular orientation to the base regardless of the drafting head movement. Drafting machines have no provisions to change the angular orientation of the drafting head from operation of a device at the base.
The invention is a SCARA type robot with counterbalanced arms and tilting base. This apparatus enables a probe to move or be positioned over an arbitrarily orientated plane. Weak or flexible foundations or footings do not affect positioning accuracy of a probe. These features make the invention very useful for on-site or portable near-field testing of antennas.
This device has significant advantages over other methods for accurate planar movement of a probe. A probe, in this case, is any end effector that only has insignificant total weight changes or force changes during any movement cycle. For example, a camera or antenna would be a probe. An end effector that picked up or placed items would be a manipulator. These advantages also apply to manipulator in place of the probe if the manipulator load is relatively small. This device is very suitable to rapid set-up and use on poorly prepared sites. Only a small pedestal base or foundation is required. Alignment is not required between separate foundations or within a large foundation. Movement of the probe does not change loads on the base and supporting structure or surface. Therefore a weak or flexible base and support does not affect the accuracy of the probe location.
Usability in poor environmental conditions is enhanced by only using rotary joints. There are no linear sliding joints, mating surfaces, or rails. It is much easier to excluded contamination from rotary joints than linear joints. Balanced arms allow the use of smaller motors, gear trains, and drive electronics.
A hinge at the base allows tilting of the probe movement plane. This allows easier and better testing of antennas (or other objects) in various orientations. The antenna does not have to be removed from its pedestal and tested in an abnormal position. The same antenna can be tested in several orientations to check for the effect of reflections from the test environment.